How to Optimize Images for eBooks

May 06, 2014

When starting an eBook project, well-written content and a
pleasing layout are of course at the top of your list. In order to
achieve this goal, you must take into consideration the
customizations and graphic settings that will need to be applied in
order for your images to display properly in the layout. Since
eBooks are becoming one of the leading formats for content
marketing, it is important to format your eBook professionally so
people will enjoy reading and navigating through the document.

In this blog, we will discuss how to optimize images for eBooks
which is one of the most important formatting steps. We will also
review the basic workflow for creating eBooks using Adobe
InDesign.

Image Resolution for eBooks

One of the most frequently
asked questions at the start of an eBook project is "what is the
minimum image resolution required when you design an eBook for the
iPad, smartphone or other eReader?" The answer is quite simple: 72
ppi. There are however some other items to keep in mind when
working with images.

Creating eBooks with InDesign

As you may know, you can drop any kind of file into InDesign: an
EPS, a Photoshop file (PSD), an Illustrator file (AI), and even
another InDesign file. All these elements will be linked and
placed, and then exported as a graphic in the ePUB.

The main goal is to avoid generating a large file. You don't
want Amazon or Apple to reject your book because of the size or
have someone spend a lot of time downloading your eBook. If you
have a few images in your file, don't worry. However, if you have
some images at 300 ppi, you don't want to export the original at
that size; it is just too large.

So, we have InDesign downsample the image when it exports. Where
can you do that? In the export options for ePUB:

Got to File > Export

Then go to the image tab of ePUB Export options.

Make sure that you have selected the default settings for image
resolution (150 ppi).

In the dropdown menu, you have the different resolution options,
but 150 ppi is a good compromise between a small file size and a
fast loading ePUB and high-res images for all those lucky
individuals with iPad retina displays. Also, check that the
"Preserve Appearance from Layout" is checked in the export options
if you want the images to be cropped like those you see in the
InDesign file.

More Options to Work with Images

InDesign also gives you the option to specify settings for
individual images or objects. The "Object Export Options" is a
great alternative if you have something that you want to handle in
a different way from the general settings. From this menu you have
the settings to change the format, resolution, quality and layout
option.

To access to the menu go to:
Object > Object Export Options…

It is worth noting that if these settings are not specified, the
ePUB export image conversion settings are used by default.

Conclusion

Keep these recommendations in mind when you are choosing the
resolution for images in your project. If you export all your
images at 72 or even 96 ppi, the images will be fuzzy and won't
look good for people with the high-res displays. So at least
specify the requirements for one image and then let InDesign do all
the downsampling. InDesign does a great job!

Comments

Nicolás Cárcano - Desktop Publishing SpecialistA native speaker of Spanish, Nicolás has expert skills on both
Mac and PC platforms with many DTP applications including Adobe
Tech Comm Suite, specifically structured and unstructured
FrameMaker, InDesign, Illustrator, Photoshop and others. He also
has advanced skills in Microsoft Office products like PowerPoint
and Word, as well as Quark.